1. Field of the Invention
This invention relates to position-based sampling systems, more particularly those systems which contain fixed resolution transducers and require non-integer modification from the resolution provided by the transducer.
2. Background of the Invention
Position-based sampling is a technique that can be applied to a broad category of systems such as printers and other imaging systems. In printers, the exposure or image is a result of image data positioned on a photoreceptor drum and ultimately onto a piece of paper or film. Imaging systems, such as night vision systems, typically use a scanner to position infrared energy onto a detector, which is then converted into a visual image via electronic processing. In both cases, the accuracy of the position from which the photoreceptor (in printers) and detector (in scanned imaging systems) sample incremental portions of the image data determines the accuracy of the image.
These types of systems may employ time-based or position-based techniques to achieve desired results. Time-based systems assume that the photoreceptor drum speed and scanner speed are constant during imaging. Positioned-based systems assume that photoreceptor drum and scanner speed are not constant and vary as a function of changing friction, wear, and speed control inaccuracies.
Since positioned-based techniques comprehend speed anomalies, they are typically more accurate than time-based systems. Positioned-based techniques rely upon the use of transducers to feed mechanical position information to tell the imaging system when to sample. Mechanical transducers with digital outputs, such as optical encoders, can be used in these applications, but they have fixed resolutions that do not necessarily match desired system resolutions. Hence, an electronic technique for converting the digital transducer resolution to the resolution desired by the system while keeping the phase relationship between transducer and converted output intact is necessary to achieve desired imaging system resolution.
For example, image data may be required to be sampled at 600 dots per inch for a printing system. However, photoreceptor position transducer information may be limited to producing 300 dots per inch. In this case, a phase-lock loop can be used to electronically increase photoreceptor position transducer data from the required sampling resolution by a factor of 2. The phase-lock loop also preserves phase integrity during the translation process and filters out high frequency noise.
In reality, the photoreceptor position information may have an effective resolution of 275.9704 dots per inch due to a mechanical photoreceptor circumference of 14.84217 inches and an optical encoder resolution of 4096 pulses per revolution. In this case, a non-integer relationship of 2.17415 exists between the photoreceptor position information and the desired sample resolution of 600 dots per inch. Since phase-lock loops are limited to integer divisions of the VCO clock output and input data, they are limited by the size of the counter/dividers used in the hardware an, therefore, cannot directly create an arbitrary, non-integer or fractional relationship between the incoming transducer data and the outgoing image data sampling rate. Traditional techniques have not addressed this non-integer scale factor problem.
Therefore, a solution is needed that provides a technique for non-integer translation resulting in a more precise relationship between input resolution and desired output resolution, while preserving phase integrity between the input and the output and filtering high frequency noise present on the input.
One aspect of the invention provides for the generation of a specified output frequency which is synchronized in position and filtered with respect to a given input frequency. The output frequency can be virtually any non-integer relationship with respect to the input frequency within the sampling constraints of the specific implementation. The invention employs an all digital closed loop system whereby the specified output frequency is directly measured and used as feedback. The direct measurement of changes in the output signal in conjunction with the closed loop architecture provides an output that accurately tracks the input and minimized quantization error.
Another aspect of the invention provides for reset/restart with minimal disturbance to loop error, allowing for a repeatable phase relationship between the output and the input from any given reset point.
Embodiments of the invention allow for a position based flashing spatial light modulator within a printer application and can be featured in a wide number of other spatial light modulator based systems as well as a myriad of unrelated implementations.
It is an advantage of the invention in that it does not require an integer relationship between the input command and the desired output frequency.
It is an advantage of the invention in that it uses the desired non-integer output frequency directly as a feedback resulting in less quantization error for superior and optimal dynamic tracking of the input.
It is an advantage of the invention in that the relationship between input and output can be easily changed within the system sampling constraints.
It is a further advantage of the invention in that it results in a more precise static relationship between the input and the desired output.
It is a further advantage of the invention to have selectable bandwidths.
It is a further advantage of the invention in that, when employed in a printer application, it can remove the need for a flywheel which is typically attached to the photoreceptor drum.